the difference is
Ralph
The fundamental difference for a subscription model service from any of the larger providers is that they already pay to manage subscriptions and distribute content etc, same with a SaaS provider, Apple arent taking over the SaaS infrastructure or client delivery.
What most of the sub model apps do is provide a way of Apple customers actually being able to use there hardware, you need to remember that the browsing experience in the iOS world is pretty poor due to the restrictions apple place on its products.
You also need to consider that most companies dont target one gadget user base so still need the infrastructure in place and with the economies of scale that they have its going to be way cheaper than paying 30% to Apple.
For example if your a newspaper with a monthly sub of £10 per month, if its collected by direct debit the cost is around 1p, debit card its 25 pence and credit card 2.5% so 25 pence. You then have your costs of distribution and your infrastructure to consider. Apple are not hosting the daily content or other items for you, they merely provide the app source so the cost of the £10 per month sub done in App is £3 per month or £36 per year, thats a lot for a sub engine compared to 12 pence per year for a direct debit.
If Apple where taking over the hosting and distribution of the content, management of the servers etc etc 30% would be fine, but for nothing more than a billing engine and an app hosting its a joke.
Its also pretty disingenious to say that Apple are bringing customers to the established brands in publishing, its actually the reverse, those brands are giving Apple users the opportunity to use there hamstrung products.